1. Field of the Invention
This invention relates to a process for the regeneration of mineral acids used to solubilize phosphate ores which thereby permits recovery of uranium and other valuable minerals from the ore.
2. Description of the Prior Art
It is well known in the phospheric acid technology that phosphate ore can be treated with a mineral acid to convert the phosphate into a soluble form, either as phosphate fertilizers, phosphoric acid or phosphoric acid compositions which can be processed into phosphate chemicals. The solubilization process also is known to dissolve impurities in the ore such as uranium and vanadium which then can be separately recovered from the resultant solution. One of the largest economic expenses of the process is the cost of the mineral acid that is consumed during the solubilization. The quantity of mineral acid required to effect the solubilization is directly related to the quantity of acid soluble materials present in the ore. Most of the acid soluble materials are dissolved in the process of solubilizing the phosphate values. No simple method is known in the prior art to regenerate the acid used to convert the phosphates into a soluble form.
Large phosphate ore fields are known to exist in Florida and in other areas of the United States. For economic reasons, only the phosphate ores containing a high ratio of phosphate to other acid soluble materials are considered commercially recoverable. The high quality commercially recoverable ores of the Florida fields have been found to contain limited quantities of uranium. The overburden on the high quality phosphate ore comprises material referred to as "leached zone material" which consists largely of sand containing components of aluminum, phosphorus, iron and other values together with clays. The leached zone material has been formed by natural weathering or leaching of the phosphate ore field. The low phosphate content of this leached ore presently makes its utilization unattractive for the production of phosphates because of the large quantity of mineral acid required to solubilize the ore. However, this leached ore has been found to contain uranium in concentrations significantly greater than in the higher quality phosphate ore that is considered commercially recoverable.
The major problem preventing the recovery of the uranium in the Florida leached zone material and from other phosphate ore fields is one of economics. A large quantity of acid is required to effect dissolution of the uranium present in these ores. The high acid requirement is due to the fact that the aluminum, phosphorus and other acid soluble values also must be dissolved to solubilize the uranium. Further, no effective method of physically concentrating the minerals to produce a significantly higher quality concentrate for treatment has been found.
Presently, the best known concentrating procedure produces a concentrate of the uranium and other phosphate minerals by scrubbing and sizing the raw ore to obtain a select fraction which then is dissolved with a mineral acid. This procedure rejects from about 60 to about 75 percent of the ore, by weight, as a coarse fraction of large particles size quartz sand and upgrades the uranium, aluminum and phosphorus content of the remainder. Acid consumption still is substantially higher than desirable. For example, 1600 to 2000 pounds of 93 to 98 percent sulfuric acid are required to dissolve 2000 pounds of concentrate. It is known that calcining the concentrate before dissolution will reduce acid consumption. However, acid consumption remains at about 600 pounds of 93 to 98 percent sulfuric acid per 2000 pounds of original concentrate.
It is desirable to provide a process that will permit regeneration of a portion of the acid that is consumed to solubilize the ore in which the uranium is present.